Swift 4可解码，直到解码时才知道密钥

Question

Swift 4 Decodable协议如何处理包含名称直到运行时才知道的键的字典？例如：

  [
    {
      "categoryName": "Trending",
      "Trending": [
        {
          "category": "Trending",
          "trailerPrice": "",
          "isFavourit": null,
          "isWatchlist": null
        }
      ]
    },
    {
      "categoryName": "Comedy",
      "Comedy": [
        {
          "category": "Comedy",
          "trailerPrice": "",
          "isFavourit": null,
          "isWatchlist": null
        }
      ]
    }
  ]

在这里，我们有一系列的字典。第一个具有键categoryName和Trending，而第二个具有键categoryName和Comedy。categoryName键的值告诉我第二个键的名称。如何使用Decodable来表达呢？

Answer 1

关键在于如何定义CodingKeys属性。虽然最常见的情况是enum它可以是符合CodingKey协议的任何内容。要创建动态键，可以调用静态函数：

struct Category: Decodable {
    struct Detail: Decodable {
        var category: String
        var trailerPrice: String
        var isFavorite: Bool?
        var isWatchlist: Bool?
    }

    var name: String
    var detail: Detail

    private struct CodingKeys: CodingKey {
        var intValue: Int?
        var stringValue: String

        init?(intValue: Int) { self.intValue = intValue; self.stringValue = "\(intValue)" }
        init?(stringValue: String) { self.stringValue = stringValue }

        static let name = CodingKeys.make(key: "categoryName")
        static func make(key: String) -> CodingKeys {
            return CodingKeys(stringValue: key)!
        }
    }

    init(from coder: Decoder) throws {
        let container = try coder.container(keyedBy: CodingKeys.self)
        self.name = try container.decode(String.self, forKey: .name)
        self.detail = try container.decode([Detail].self, forKey: .make(key: name)).first!
    }
}

用法：

let jsonData = """
  [
    {
      "categoryName": "Trending",
      "Trending": [
        {
          "category": "Trending",
          "trailerPrice": "",
          "isFavourite": null,
          "isWatchlist": null
        }
      ]
    },
    {
      "categoryName": "Comedy",
      "Comedy": [
        {
          "category": "Comedy",
          "trailerPrice": "",
          "isFavourite": null,
          "isWatchlist": null
        }
      ]
    }
  ]
""".data(using: .utf8)!

let categories = try! JSONDecoder().decode([Category].self, from: jsonData)

（我isFavourit将JSON 更改为，isFavourite因为我认为这是拼写错误。如果不是这种情况，则很容易修改代码）